The present invention relates to method and apparatus for measuring size and three-dimensional shape (hereinafter simply referred to as shape) of fine patterns and more particularly, to method and apparatus suitable for measurement of the size and shape of fine patterns formed in, for example, semiconductor devices such as semiconductor memory and integrated operation circuit.
For measurement of the width of a fine pattern formed in the semiconductor device, a technique based on a measuring SEM (scanning electron microscope) has been known, according to which an electron beam is irradiated on a target or object pattern and secondary electrons and reflected electrons generated from the pattern are detected to use intensity of detection signals. In the measuring SEM, however, observation is made from above the measuring object, so that a fine width of the object pattern can be measured but a three-dimensional shape including height of the object pattern cannot be measured. In the past, for measurement of the three-dimensional shape, a method has generally been employed in which a target portion of circuit pattern in a semiconductor device formed on a semiconductor wafer is either cut or shaved with an FIB and a resulting section is observed with an electron microscope, for instance.
But, the measurement based on the measuring SEM or section observation as above faces problems that the throughput is decreased as compared to that obtained through optical measurement based on, for example, a microscope and the measuring apparatus is complicated and costly.
Meanwhile, to eliminate the problems as above, a method called scatterometry has been proposed, according to which an optical measuring method is used to measure size and shape of fine patterns in a non-contact and nondestructive fashion. This method is described in the specification of, for example, U.S. Pat. No. 5,867,276. To describe this method in brief, reference is made to FIG. 2 showing the general construction of a spectroscopic measuring apparatus.
In the figure, an incandescent light beam from an incandescent light source 3 is passed through an objective lens 4 so as to be irradiated, as incident light beam 5, onto a measuring point 10 on a semiconductor wafer 1. The incident light beam 5 is irradiated at a specified incident angle onto the semiconductor wafer 1 and a reflected light beam 6 at a reflection angle optically symmetrical to the incident angle is condensed by a condenser lens 7 and received at a light receiver 8. The received light beam from the light receiver 8 is spectroscopically analyzed by means of a spectroscope 9 so that reflection intensity at the measuring point 10 may be measured in relation to individual wavelengths.
The semiconductor wafer 1 representing a measuring object is mounted on a stage 2 movable in X, Y and Z directions and rotational direction (θ). Therefore, the light beam can be irradiated at a desired spot on the wafer 1 by moving the stage 2 in X, Y and Z directions and spectrum waveforms at different angles θ to the same measuring point can be detected.
FIG. 3 shows graphically results of measurement of spectra distribution 11 by means of the apparatus constructed as above and in the figure, abscissa represents the wavelength and ordinate represents the measured intensity of reflected light.
Incidentally, when semiconductor chips 12 are arranged on the semiconductor wafer 1 as shown in FIG. 4A, for instance, it is general to provide a chip main part or proper 13 and scribe regions 14 and 15 in the semiconductor chip 12 as shown in FIG. 4B. Formed in the chip proper 13 are fine patterns (actual patterns) of semiconductor device such as semiconductor memory and integrated operation circuit and disposed in the scribe regions 14 and 15 are patterns (test patterns) for testing fabricated through the same process as the actual patterns. After the semiconductor wafer 1 is completed and individual semiconductor chips 12 are diced, the scribe regions 14 and 15 used for measurement of patterns are removed from the semiconductor chip 12 by dicing.
An example of a test pattern in each of the scribe regions 14 and 15 in FIG. 4B is illustrated in perspective view form in FIG. 5.
The pattern shown in the figure is exemplified as a pattern generally called line and space in which structurally, a linear pattern line 16L and a space portion 16S are arranged alternately.
In the previously-described scatterometry method, the test pattern as above is handled as an object and when a plurality of modeled pattern shapes (model patterns) are assumed, a scattered light intensity distribution practically detected by using the optical measuring apparatus as shown in FIG. 2 is compared with scattered light intensity distributions for individual model patterns obtained through an optical simulation, whereby a model pattern for which the both types of scattered light intensity distributions coincide with each other is determined as a shape of the test pattern representing the object to be measured.
For example, when the line and space as shown in FIG. 5 is determined as a measuring object pattern, a model pattern (profile) 17 of sectional (three-dimensional) shape as shown in FIG. 6 is set up or established. This model pattern 17 consists of a line portion 18 and a space portion 19 and for example, top width Wt, intermediate width Wm, bottom width Wb, top shoulder roundness Rt, bottom angle Ab and height Hc are set as shape parameters of this measuring target pattern.
Then, by determining upper and lower limits and step values of the individual parameters and setting a plurality of values, which differ stepwise in accordance with the step values between the upper and lower limits, in respect of the individual parameters, model patterns 17 corresponding to all combinations of the parameter set values are assumed and scattered light intensity distribution as shown in FIG. 3 is determined through calculation in respect of each model pattern 17 so as to be recorded as a library for use in the comparison described so far.
As will be seen from the above, the scatterometry method is basically for optical measurement and therefore, has advantages that the measuring apparatus is simpler and cheaper than the SEM measurement and besides the throughput is higher.
But, on the other hand, because of the fact that uniform repetitive patterns of about 50 μm square are needed as measuring target patterns in order to maintain quantities of light sufficient for detection and a huge number of model pattern shapes need be generated on a computer and scattered light intensity distribution for each model pattern must be calculated by the computer in order to obtain highly accurate measurement results, there arises a problem at present that the model pattern shapes and their scattered light intensity distributions can be generated within practically acceptable time in connection with only the patterns of linear line and space shape as shown in FIG. 5.